In a typical wireless telecommunications network, a “softer handoff” may be performed when a mobile station switches to a different sector of the same base transceiver station (BTS) that it is currently using. Furthermore, a “soft handoff” may be performed if the mobile station switches to a different sector of a different BTS than it is currently using. During soft and softer handoffs, the new sector that the mobile station uses may employ the same carrier frequency as the previous sector. Thus, the mobile station may use the same carrier frequency for communications after the handoff.
A problem may arise, however, if a new sector does not employ the same carrier frequency as the sector from which the mobile station came. This often occurs, for instance, when a mobile station moves from a city area into a rural area where fewer carriers are provided. Additionally, a problem may arise if an assigned frame selector (e.g., identification value) for a call changes, which may occur when a mobile station moves from one market to another (e.g., the mobile station connects to a different mobile switching center (MSC)).
Prior art systems have typically used “hard handoff” techniques as solutions to these problems. Examples of typical hard handoff techniques include Pilot Beacon Hard Handoff, Round Trip Delay Hard Handoff, Hard Handoff based on Frame Error Rate (FER), Data based Assisted Hard Handoff (DAHO), and Non Pilot Assisted Directed Frequency Hand Over.
In hard handoff techniques such as these, a call is broken before a new connection that uses a different carrier frequency is made. Although the new connection is preferably made quickly (i.e., before the call disconnects or is noticeably disrupted), these hard handoff techniques may face a number of drawbacks. First, such hard handoff techniques may require network vendor specific solutions and the coupling of disparate vendor systems. Thus, these techniques may be relatively expensive and difficult to integrate. Furthermore, hard handoff techniques may require additional hardware having a complicated setup. In addition, the very nature of hard handoffs (i.e., breaking a connection before making a new one) typically causes such systems to have low reliability and a relatively high call drop rate.